The present invention relates to an improvement of an electrically operated automatic focalizing camera. More specifically, the invention relates to a device for preventing erroneous operation of the camera due to conditions of an object to be photographed.
A variety of electrical focus detecting devices have been proposed in the art. The relation between focus detection output and the distance by which the lens has been extended in such a device is as indicated in FIG. 1. In FIG. 1, the vertical axis represents the focus detection output and the horizontal axis represents the lens extending distance or amount. Furthermore, in the graph shown in FIG. 1, the peaks A, B and C indicate three objects positioned at different distances from the camera. In the case when distance to an object is determined using such a signal, a technique has been employed in which a certain level (indicated by l in FIG. 1) is chosen and peaks higher than the level are detected. However, if a focalization indicating device is used, then focalization indication is provided for the peaks A and C even though the desired object corresponds to the peak B for instance. Furthermore, with an automatic focalizing device, the lens will be set for the peak C in a system in which only the maximum peak is detected or the lens will be set for the peak A or C in a system in which the lens extension is carried out using the closest focusing distance or starting from infinity with the first peak from that position detected. In none of the systems can the lens be focused on the intended object. There are many examples of such objects, for instance, animals in a cage and people in a crowd.
Accordingly, an object of this invention is to provide an electrical focus detecting device which can be used for objects as described above by presetting an object distance at which focus detection is to be performed.